1. Field of the Invention
The present invention relates to a method for producing a glycol ether. Particularly, the present invention relates to a method for producing a glycol ether, which comprises reacting an alkylene oxide with an alcohol in the presence of a catalyst.
2. Discussion of Background
Glycol ethers are useful as solvents for paints or inks, as components to be incorporated into brake fluids or as intermediates for producing glycol ether acetates. They are produced usually by reacting alkylene oxides with alcohols in the presence of homogeneous base catalysts such as alkali-metal hydroxides or amines (see the following reaction schemes (i) and (ii)). ##STR1##
Among compounds formed by the reactions (i) and (ii), the most commercially valuable compound is usually the terminal-adduct (3). However, when the above homogeneous base catalyst is employed, there is a drawback that an adduct having at least 2 mol of an alkylene oxide added, as shown by the formula (5), is likely to form. Further, it is generally difficult to remove the homogeneous catalyst from the system in the purification process. In a case where an asymmetrical alkylene oxide such as propylene oxide is employed, there is a problem such that it is difficult to control the positional selectivity of the reaction and to preferentially obtain the desired terminal adduct (3).
Further, the internal adduct (4) which is a position isomer of the terminal adduct (3), to be formed by the above reactions might possibly show toxicity, and its separation and removal will be required, so that the yield of the terminal adduct tends to be low, and the number of process steps increases, such being undesirable from the economical viewpoint.
To solve such problems, some methods have been proposed for producing glycol ethers by using solid bases as catalysts.
For example, Japanese PCT Publication JP-A-5-503946 discloses a method for producing glycol ethers, wherein an anionic double hydroxide is used as a catalyst.
Further, Japanese Unexamined Patent Publication JP-A-61-204142 discloses a method for producing glycol ethers, wherein an anion exchange resin containing a primary, secondary or tertiary amino group or a secondary or tertiary amino group having a substituent, is used as the catalyst. In an Example of this publication, it is disclosed that when propylene oxide and ethanol were reacted glycol ether was formed at a conversion of 85%.
However, such anion exchange resins generally had a problem in the life of the catalysts, since their heat stability is low as compared with cation exchange resins, and their durability was accordingly poor.
The present inventors have conducted extensive studies taking the above described related art into consideration and as a result, have found that by employing an anion exchange resin having a certain specific structure as the catalyst, not only the problem with respect to the durability of the catalyst can be solved, but also it is possible to produce glycol ethers having a terminal-adduct type structure at high reactivity and selectivity. The present invention has been accomplished on the basis of this discovery.